A
Kessler Syndrome if we're not careful, which could render most or all orbits useless.
the mention of a
Laser Broom. I've got to wonder how practical that would be.
Kessler Syndrome, as bad as it could get, would not be a permanent condition, but there's very little discussion of how long it would last. It may last hundreds of years or possibly longer, but not for millennia.
Orbits decay, and how long they take to decay is a function of orbit height, which itself is a function of velocity. If LEO was in a state of Kessler Syndrome, those orbits would become available again for use faster than the condition in higher orbits. And if Kessler Syndrome was confined to LEO, the higher orbits wouldn't be affected, though the opposite is not true. A Kessler Syndrome in higher orbits would eventually encompass all lower orbits.